1. Field of the Invention
The present invention relates to a surface-mount antenna and communication apparatus using the same which are used in a radio local area network (LAN) and mobile communication equipment such as a portable telephone.
2. Description of the Related Art
FIG. 8 shows a conventional .lambda./4 surface-mount antenna. Through holes 22 and 23 are provided between one pair of end faces 21a and 21b in a base member 21. A first radiation electrode 24 and a second radiation electrode 25 are formed at the inside surfaces of the through holes 22 and 23, respectively. One end of the first radiation electrode 24 is connected to one end of a pattern electrode 26 formed on one end face 21a, and the other end of the first radiation electrode 24 serves as an open end 24a on the other end face 21b. One end of the second radiation electrode 25 is connected to the other end of the pattern electrode 26, and the other end of the second radiation electrode 25 is connected to a ground terminal 27 formed on an end face 21b in the base member 21.
There is also shown a power-supplying terminal pin 28. A metal pin 28b electrically connected to a power supplying terminal 28a is covered with resin 28c. The power supplying terminal pin 28 is inserted into the through hole 22 having the first radiation electrode 24 to form a capacitor between the metal pin 28b and the first radiation electrode 24 with the resin 28c serving as a dielectric. With this capacitor, a high-frequency signal is electromagnetically coupled with the first radiation electrode 24 to cause the high-frequency current to flow to the ground through the first radiation electrode 24, the pattern electrode 26, and the second radiation electrode 25. With this configuration, a radio wave is emitted.
In the conventional surface-mount antenna, the coupling level between the power supplying terminal pin 28 and the first radiation electrode 24 depends on how the power supplying terminal pin 28 is inserted into the first radiation electrode 24. The manner in which the terminal pin 28 is inserted may cause a frequency change. Therefore aging or dropping of the antenna causes a large frequency shift. Furthermore, since the power supplying terminal pin 28 is required, the antenna becomes large and is prevented from being made compact.
Electromagnetic coupling between the power supplying terminal pin 28 and the first radiation electrode 24 needs to be weak. Since the coupling is made at a high voltage, the level of coupling is difficult to adjust.
A communication apparatus using such a conventional surface-mount antenna also has the same drawbacks as a surface-mount antenna.